1. Field of the Invention
This invention relates to a method for extracting salt from process streams, and more specifically this invention relates to a method for using a membrane-based process to enable the recovery and recycling of acid and base from a corresponding salt from aqueous process streams which also contains organic material.
2. Background of the Invention
Process streams containing a myriad of salts, inorganic compounds and organic compounds are common industrial effluents. For example, in the propylene ammoxidation process which produces acrylonitrile, ammonia and dilute sulfuric acid is used to prevent propylene combustion and to quench the reaction, respectively. Ultimately, an ammonium sulfate waste-stream contaminated with organics is produced. This quench stream containing ammonium sulfate and organics such as acrylic acid, amide and other nitriles is the major waste water stream from the process.
Other major petrochemical processes, such as caprolactam production via the Beckman rearrangement process, and methacrylate production via acetone conversion, and the production of many other intermediate or specialty chemicals, also produce waste water containing ammonium salts contaminated with organics.
Aside from ammonium salt presence, other salts also pose problems. In the production of polycarbonates, via bisphenol conversion for example, a contaminated sodium chloride waste stream is produced and sodium hydroxide is used in the process. In bioprocessing, the manufacture of several organic acids such as citric, gluconic, lactic acid, plus the manufacture of the amino acids such as lysine, alanine, valine, leucine, proline, methionine and generally the essential and nonessential amino acids produce waste salts, or gypsum in the conventional recovery process. In the pharmaceutical and fine chemical manufacturing industry, waste stream constituent recovery and purification problems also exist, for example in salicylic acid production.
Processes exist for the purification of bases from materials containing base and salt, such processes disclosed in U.S. Pat. Nos. 5,135,626 and 5,228,962 to Mani et al. However, these process are designed to recover salts from streams containing excess base and/or acid.
Other processes, such as those disclosed in U.S. Pat. Nos. 4,740,281, 4,999,095, 5,198,086 and 5,200,046 to Chlanda et al., disclose the use of bi-polar membranes to electrodialytically convert salts to their respective acids and bases. However, these and other disclosures generally deal with the use of such membranes to reclaim acids and bases from inorganic pickling liquors. U.S. Pat. No. 5,352,345 to Byszewski et al. discloses a process whereby a combination of electrodialysis units are employed to reclaim exhausted regenerating solutions used to regenerate ion exchange gels and resins. Generally, the prior art does not address the significant problem of the presence and removal of organic contaminants from waste streams which contain salts, and in fact, given the nature of bipolar membranes, the prior art tends to teach away from reclaiming salts found in contaminated streams.
A need exists in the art for an economical process to recover, purify and convert salts in waste water streams into their respective acids and bases. The process would also enhance the biological treatability of any organic contaminants contained in the waste streams.